Decreasing Transpiration and the Effect Upon Growth

According to a simple but reliable theory, transpiration can be decreased with a certain, but relatively smaller, decrease in photosynthesis. The challenge is to accomplish this in practice or even to decrease transpiration without an accompanying decrease in photosynthesis. This chapter reviews the simple theory, describes some natural ways that transpiration is decreased, examines artificial means of decreasing transpiration and its effect on photosynthesis, and describes an experiment in stomatal closure of maize. Stomatal closure is an alternative means of decreasing transpiration, and its theoretical effect on photosynthesis can be seen in a similar way. The natural operation of the stomatal hydrostat is undoubtedly at the heart of the increase in the wilting percentage in the soil that accompanies increased transpirational demand. In a real canopy of plants, stomatal resistance may be a smaller proportion of the whole resistance that governs transpiration than it is in a single leaf.